Optical characterization of the organic matter of an Andisol of the East of Antioquia, Colombia

Abstract

The optical characterization of the organic matter (OM) of an Andisol obtained from selective and sequential extractions of Al, Fe and Si (potassium chloride, sodium pyrophosphate, ammonium acid oxalate, dithionite-citrate-bicarbonate and sodium hydroxide) was made. From the absorbances the E4/E6 ratio, the Δ log K, the Melanic Index (MI) and the ODOE were calculated. The behaviors of the E4/E6 ratio, the Δ log K and the MI in the extracts obtained with sodium pyrophosphate and with ammonium acid oxalate showed a higher degree of humification for the organic matter extracted from the A and 2B/A horizons and one smaller for the one extracted from the 3C/A and 4Bs horizons. The ODOE showed the presence of organic complexes in the extracts obtained with pyrophosphate and with sodium hydroxide and the iluvial accumulation of non-crystalline Fe oxides and hydroxides in the 4Bs horizon in the extract obtained with ammonium acid oxalate. In the horizon A, the humification indexes marked a change in the degree of evolution of the MO between 8 and 10 cm of depth, which could indicate the presence of a lithological discontinuity or of buried soil.

Keywords

• Andisol
• caracterización óptica
• materia orgánica
• índices de humificación
• extracciones selectivas de Al, Fe y Si.